Method for producing garnet type oxide solid electrolyte

Abstract

A method for producing a garnet type oxide solid electrolyte that is inhibited from a reaction of a flux and a crucible in heating and from a contamination with a crucible component produced by the reaction. The method for producing a garnet type oxide solid electrolyte represented by a general formula (Lia1, Aa2)La3-bEbZr2-cMcO12 may comprise the steps of: preparing raw materials for the garnet type oxide solid electrolyte at a stoichiometric ratio of the above general formula; preparing flux raw materials by using NaCl and KCl at a molar ratio of NaCl:KCl=x:(1−x) where x satisfies 0≤x≤1; mixing the solid electrolyte raw materials prepared in the above step and the flux raw materials prepared in the above step; and heating a mixture of the solid electrolyte raw materials and the flux raw materials at a temperature of less than 1100° C.

The invention claimed is: 
     
       1. A method for producing a garnet type oxide solid electrolyte represented by a general formula (Li a1 , A a2 )La 3-b E b Zr 2-c M c O 12  where a1 satisfies 5<a1<7; a2 satisfies 0≤a2≤0.2; b satisfies 0≤b≤1; c satisfies 0.125≤c≤0.6; A is at least one element selected from Al and Ga; E is at least one element selected from Ca and Sr; and M is at least one element selected from Nb and Ta,
 the method comprising the steps of: 
 preparing raw materials for the garnet type oxide solid electrolyte at a stoichiometric ratio of the above general formula; 
 preparing flux raw materials by using NaCl and KCl at a molar ratio of NaCl:KCl=x:(1−x) where x satisfies 0≤x≤1; 
 mixing the solid electrolyte raw materials prepared in the above step and the flux raw materials prepared in the above step; and 
 heating a mixture of the solid electrolyte raw materials and the flux raw materials at a temperature of less than 1100° C., 
 
       wherein the flux excludes a lithium-containing compound. 
     
     
       2. The method for producing the garnet type oxide solid electrolyte according to  claim 1 , wherein x satisfies 0≤x<1. 
     
     
       3. The method for producing the garnet type oxide solid electrolyte according to  claim 2 , wherein x satisfies 0.1≤x≤0.8. 
     
     
       4. The method for producing the garnet type oxide solid electrolyte according to  claim 1 , wherein the solid electrolyte raw materials and the flux raw materials are mixed so that a theoretical value of a molar concentration of the solid electrolyte in the dissolved mixture after synthesis, is 2.5 mol/L or less in the heating step. 
     
     
       5. The method for producing the garnet type oxide solid electrolyte according to  claim 1 , wherein a1 is in a range of from 5.8 to 6.75 and c is in a range of from 0.125 to 0.375. 
     
     
       6. The method for producing the garnet type oxide solid electrolyte according to  claim 1 , wherein the garnet type oxide solid electrolyte is represented by one of the following general formulae:
 Li 6.4 La 3 Zr 1.4 Nb 0.6 O 12 , Li 6.39 Ga 0.12 La 3 Zr 1.75 Nb 0.25 O 12 , Li 6.75 La 3 Zr 1.75 Nb 0.25 O 12 , Li 6.15 Al 0.2 Zr 1.75 Nb 0.25 O 12 , Li 6.15 Ga 0.2 La 3 Zr 1.75 Nb 0.25 O 12 , Li 6.28 Ga 0.04 La 3 Zr 1.4 Nb 0.6 O 12 , and Li 6.28 Al 0.04 La 3 Zr 1.4 Nb 0.6 O 12 .